Code P0500: Vehicle Speed Sensor A Circuit, help?

[zipper228]

Hoping someone can help me narrow this down:
Failed smog recently due to incomplete OBDII readiness, due to this fault code, P0500: Vehicle Speed Sensor A Circuit

Cleaned all 4 sensors (back two were filthy) and visually inspected the wiring; all looked to be ok. Cleared the code, tried to complete the drive cycle but code returned.
I'm guessing at this point that one or more sensors need replacement but not sure which. Does anything in that code indicate whether its the front or back sensors that are malfunctioning? I'm guessing "A Circuit" could be meaningful but can't seem to find any info to confirm